Hydrocarbons that are in a gaseous state at atmospheric pressure and room temperature (e.g. 20° C.), are often transported as cold hydrocarbons, as by ship in liquid form such as LNG (liquified natural gas), at atmospheric pressure and −160° C. Another form of cold gaseous hydrocarbons that are ship-transported are hydrates (gas entrapped in ice). At the ship's destination, the LNG (or other gas) may be heated and flowed to an onshore distribution facility. Proposed prior art offloading stations have included a fixed platform extending up from the sea floor to a height above the sea surface and with a regas unit on the platform for heating the LNG. Because of fire dangers in dealing with LNG, rigid platforms, which minimize flexing joints, have previously been proposed for offloading LNG from a tanker and heating it to gassify it.
The cost of a fixed platform is high even at moderate depths, and at increasing depths (e.g. over 50 meters) the costs of fixed platforms increase dramatically. In addition, if the platform lies in an open sea it is difficult to moor a tanker to the platform because the tanker shifts position and heading with changing winds, waves and currents. An offshore LNG offloading and regas station which avoided the use of fixed platforms, and which provided the high reliability demanded in LNG offloading, heating and storage, would lower the cost of such stations and allow them to be used in situations where they previously were uneconomical.